TWO young sisters taken away from their biological mother and handed over to her former lesbian partner must be given back, the Law Lords ruled yesterday.

The "bitter dispute" between the two women over the custody of two girls aged seven and five reached the highest court in the land after three judges at the Court of Appeal agreed the mother should not be the primary carer.

Lord Justice Thorpe, in what was hailed at the time as a landmark ruling for same-sex relationships, said in the eyes of a child the natural parent may not be a biological one.

But today five Law Lords who sit at the House of Lords came down strongly in favour of preferring the biological mother when deciding who should get custody.

Lord Nicholls of Birkenhead, reversing the decisions of both the Court of Appeal in April this year and of a High Court Family Division judge, said the welfare of the child should be the court's paramount consideration.

"In reaching its decision the court should always have in mind that, in the ordinary way, the rearing of a child by his or her biological parent can be expected to be in the child's best interest, both in the short term and also, and importantly, in the longer term.

"I decry any tendency to diminish the significance of this factor. A child should not be removed from the primary care of his or her biological parents without compelling reason."

None of the parties involved in the case can be identified, other than by initials, to protect the children.